Fuel cell header wedge

ABSTRACT

A fuel cell system may include a fuel cell stack having a header and active area in fluid communication with the header. The fuel cell system may also include a wedge disposed within the header and configured to alter the cross-sectional area of the header along the length of the stack such that, during operation of the stack, a flow velocity of gas through the active area is generally constant.

BACKGROUND

Uniform gas and coolant distribution may improve the performance ofProton Exchange Membrane (PEM) fuel cell systems while reducing balanceof plant requirements. As the number of cells in a stack increases,however, creating uniform gas flow conditions throughout the stack maybecome difficult. Gas flow variation in a 400 cell fuel cell stack, forexample, may cause lower gas velocities in some cells and higher gasvelocities in other cells. The reduced flow in some cells may result inlower current densities or cell flooding. Similarly, excessive flow canalso lead to durability concerns within the fuel cell stack.

SUMMARY

A power generating system may include a plurality of bipolar platesstacked to form a fuel cell assembly having an inlet header and a wedgedisposed within the inlet header. The wedge may be configured to alterthe cross-sectional area of the inlet header along the length of thefuel cell assembly and/or engage the plates to align the plates.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of an embodiment of a fuel cell assembly.

FIG. 2 is a front view of a bipolar fuel cell plate.

FIG. 3 is a rear view of the bipolar fuel cell plate of FIG. 2.

FIG. 4 is a perspective view of an embodiment of a fuel cell headerwedge.

FIG. 5 is a perspective view of another embodiment of a fuel cell headerwedge.

FIG. 6 is an exploded assembly view of a portion of the fuel cellassembly of FIG. 1.

FIG. 7 is an assembly view of the portion of the fuel cell assembly ofFIG. 6.

FIG. 8 is an example plot of gas velocity versus plate number from inletfor fuel cell assemblies with and without wedges.

DETAILED DESCRIPTION

Referring to FIG. 1, an embodiment of a fuel cell assembly 10 includes aplurality of stacked bipolar fuel cell plates 12, end plates 14, 16, andclamps 18. The stacked fuel cell plates 12 form a fuel cell stack 20.The end plate 14 includes inlet and outlet ports (not shown).

Gases, such as hydrogen and air, enter the fuel cell stack 20 via theinlet ports and exit the fuel cell stack 20 via the outlet ports (asindicated by arrow). Coolant also enters the fuel cell stack 20 via oneof the inlet ports and exits the fuel cell stack 20 via one of theoutlet ports.

As known in the art, electrical energy may be generated by the fuel cellstack 20 as the hydrogen and oxygen react. This electrical energy may beused to power various electrical devices and/or stored within an energystorage unit.

The fuel cell stack 20 of FIG. 1, for example, is configured to providemotive power for a vehicle 22. That is, the fuel cell stack 20 iselectrically connected in a known fashion with an electric machine (notshown) that converts electrical energy generated by the fuel cell stack20 to mechanical energy used to move the vehicle 22. Alternatively, thefuel cell stack 20 may be electrically connected with a battery (notshown) as mentioned above to store electrical energy generated by thefuel cell stack 20. An electric machine may be configured in a knownfashion to draw electrical energy from the battery to produce mechanicalenergy used to move the vehicle 22. Other arrangements are, of course,also possible.

Referring to FIGS. 2 and 3, a bipolar fuel cell plate 12 may includeinlet header surfaces 24, 26 defining, respectively, fluid passageways28, 30, inlet coolant surface 32 defining coolant passageway 34, inlettransition areas 36, 38, and active areas 40, 42. The bipolar fuel cellplate 12 may also include outlet header surfaces 44, 46 defining,respectively, passageways 48, 50, outlet coolant surface 52 definingcoolant passageway 54, and outlet transition areas 56, 58. Anysuitable/known plate arrangement, however, may be used.

A gas, such as hydrogen, may flow through the fluid passageway 28 (whichis in fluid communication with an inlet port of the end plate 14 ofFIG. 1) and enter the inlet transition area 36 via feed passageways 37that fluidly connect the fluid passageway 28 and the inlet transitionarea 36. The inlet transition area 36, as known in the art, distributesthe hydrogen across the plate 12 via walls 29 prior to entering theactive area 40 by way of openings 39 that fluidly connect the inlettransition area 36 and active area 40. (Hydrogen within the active area40 may then travel along channels 31 defined by walls 33.)

Hydrogen may exit the active area 40 by way of openings 41 that fluidlyconnect the active area 40 and the outlet transition area 56. The outlettransition area 56, as known in the art, directs the hydrogen via walls35 toward return passageways 43 that fluidly connect the outlettransition area 56 and fluid passageway 48 (which is in fluidcommunication with an outlet port of the end plate 14 of FIG. 1).

Air may flow through the fluid passageway 30 (which is in fluidcommunication with an inlet port of the end plate 14 of FIG. 1) andenter the inlet transition area 38 via feed passageways 45 that fluidlyconnect the fluid passageway 30 and the inlet transition area 38. Theinlet transition area 38 distributes the air across the plate 12 viawalls 53 prior to entering the active area 42 by way of openings 47 thatfluidly connect the inlet transition area 38 and active area 42. (Airwithin the active area 42 may then travel along channels 55 defined bywalls 57.)

Air may exit the active area 42 by way of openings 49 that fluidlyconnect the active area 42 and the outlet transition area 58. The outlettransition area 58 directs the air via walls 59 toward returnpassageways 51 that fluidly connect the outlet transition area 58 andfluid passageway 50 (which is in fluid communication with an outlet portof the end plate 14 of FIG. 1).

A coolant, such as water, may flow through the fluid passageway 34(which is in fluid communication with an inlet port of the end plate 14of FIG. 1) and enter a gap (not shown) within the bipolar fuel cellplate 12. This gap separates the transition areas 36, 56 and active area40 from the transition areas 38, 58 and active area 42 by way ofopenings (not shown) that fluidly connect the fluid passageway 34 andthis gap. Water may exit the gap by way of openings (not shown) thatfluidly connect the gap and the fluid passageway 54 (which is in fluidcommunication with an outlet port of the end plate 14 of FIG. 1).

As mentioned above, the pressure within, for example, the fluidpassageway 28 may be higher the closer the bipolar fuel cell plate 12 ispositioned relative to the hydrogen inlet port of the end plate 14 (FIG.1). The pressure within the fluid passageway 28 may be lower the furtheraway the bipolar fuel cell plate 12 is positioned relative to thehydrogen inlet port of the end plate 14. The same may be true forpressures within the fluid passageways 30.

This plate to plate difference in pressure gradients within the inletheaders that may depend on where the plate 12 is located relative to theinlet ports of the end plate 14 (FIG. 1) may result in non-uniform gasflow through the active areas 40, 42 along the length of the fuel cellstack 20 (FIG. 1). That is, the active areas 40, 42 of the plates 12located proximate to the end plate 14 may have gas flow velocities thatare greater than those of the active areas 40, 42 of the plates 12located proximate to the end plate 16.

Referring to FIG. 4, an embodiment of a fuel cell header wedge 60 mayinclude a thin end 62 and a thick end 64 opposite the thin end 62. Inthe embodiment of FIG. 4, the wedge 60 has a generally rectangular shape(designed to mate with, for example, portions of the inlet headersurfaces 24, 26 of FIGS. 2 and 3) and tapers from the thick end 64 tothe thin end 62. The wedge 60, in other embodiments however, may take onany suitable shape and/or size depending on, for example, flowcharacteristics associated with the fuel cell stack 20 (FIG. 1), designconsiderations, etc. As discussed in further detail below, the wedge 60may be positioned within the fuel cell stack 20 to alter thecross-sectional areas of (and thus the pressure gradients within) eitherof the fluid passageways 28, 30 and/or align the plates 12 (FIG. 1) ofthe fuel cell stack 20.

Referring to FIG. 5, another embodiment of a fuel cell header wedge 66has a generally rectangular shape (designed to mate with, for example,portions of the outlet header surfaces 44, 46 of FIGS. 2 and 3) and agenerally uniform thickness. As discussed in further detail below, thewedge 66 may be positioned within the fuel cell stack 20 (FIG. 1) toalign the plates 12 (FIG. 1) of the fuel cell stack 20.

Referring to FIG. 6, a portion of the fuel cell assembly 10 is shownexploded. As apparent to those of ordinary skill, the fluid passageways28, 30 associated with each of the plates 12 collectively formrespective inlet headers (defined, respectively, by the inlet headersurfaces 24, 26 of each of the plates 12). Likewise, the fluidpassageways 48, 50 associated with each of the plates 12 collectivelyform respective outlet headers (defined, respectively, by the outletheader surfaces 44, 46 of each of the plates 12). Similarly, (i) theinlet transition areas 36 of each of the plates 12 may collectivelydefine an inlet (hydrogen) transition area of the fuel cell stack 20,(ii) the inlet transition areas 38 of each of the plates 12 maycollectively define an inlet (air) transition area of the fuel cellstack 20, (iii) the active areas 40 of each of the plates 12 maycollectively define an active (hydrogen) area of the fuel cell stack 20,and (iv) the active areas 42 of each of the plates 12 may collectivelydefine an active (air) area of the fuel cell stack 20, etc.

In this example, the wedge 60 resides within the inlet header formed bythe fluid passageways 28 of each of the plates 12, with the thick end 64disposed adjacent to the end plate 16 and the thin end 62 disposedadjacent to the end plate 14 (not shown). The tapered shape of the wedge60 effectively reduces the cross-sectional area of the inlet headeralong the fuel cell stack 20 as the wedge 60 becomes thicker so as tocompensate for any loss in gas volume associated with being further awayfrom the inlet ports associated with the end plate 14. Additionally,because the wedge 60 is generally shaped to mate with portions of theinlet header surfaces 24 defining the inlet header, the wedge 60 mayassist in aligning the plates 12 during assembly and keeping the plates12 aligned during operation.

The wedge 66 resides within the outlet header formed by the fluidpassageways 48. Because the wedge 66 is generally shaped to mate withportions of the outlet header surfaces 46 defining the outlet header,the wedge 66 may likewise assist in aligning the plates 12 duringassembly and keeping the plates 12 aligned during operation.

Referring to FIG. 7, the wedges 60, 66 are shown in place. In otherexamples, the wedge 60 may reside within either (or both) of the inletheaders formed by the fluid passageways 28, 30. Likewise, the wedge 66may reside within either (or both) of the outlet headers formed by thefluid passageways 48, 50, etc.

The wedges disclosed herein may be formed or manufactured in anysuitable fashion. For example, the wedge 60 may be molded in plastic ormachined from suitable metal stock. Alternatively, the wedge 60 may beformed in place. Lubricated removable gates may be inserted into theinlet headers along with stops designed into the end plates 14, 16. Anepoxy resin, for example, may then be applied. After hardening, thelubricated removable gates may be removed. Other techniques andscenarios are also possible.

The gas velocity versus plate number from inlet was analyzed usingcomputational fluid dynamic techniques for fuel cell assemblies similarto those described herein. In a first simulation, the fuel cell assemblyanalyzed lacked wedges as described herein. In a second simulation,wedges similar to those described with reference to FIGS. 4 and 5 wereincluded in the fuel cell assembly analyzed.

Referring to FIG. 8, a comparison of the gas velocity versus platenumber from inlet is depicted for the simulations. The introduction ofthe wedge appears to reduce the variation in gas velocity through theactivate area along the fuel cell assembly relative to circumstanceswhere the wedge is absent. For example, the standard deviation invelocity distribution dropped from 0.087 m/s (without the wedge) to0.0379 m/s (with the wedge).

While embodiments of the invention have been illustrated and described,it is not intended that these embodiments illustrate and describe allpossible forms of the invention. The words used in the specification arewords of description rather than limitation, and it is understood thatvarious changes may be made without departing from the spirit and scopeof the invention.

What is claimed:
 1. A vehicle comprising: a fuel cell system forproviding power to move the vehicle and including a fuel cell stackhaving a header and active area in fluid communication with the headerand a wedge inserted within the header parallel to gas flow through theheader and configured to alter a cross-sectional area of the headeralong an entire length of the header such that, gas flow through theactive area is generally constant.
 2. The vehicle of claim 1 wherein thewedge is tapered.
 3. The vehicle of claim 2 wherein the fuel cell stackfurther has a gas inlet side, wherein the wedge has a thick end and athin end, and wherein the thin end of the wedge is disposed proximate tothe gas inlet side.
 4. The vehicle of claim 1, wherein the fuel cellstack further has another header and wherein the fuel cell systemfurther includes another wedge disposed within the another header. 5.The vehicle of claim 4 wherein the another wedge has a generallyrectangular shape.